image quality 2 prelim

image quality 2 prelim - 3.0 Basic Imaging PrinciplesImage...

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3.0 Basic Imaging Principles—Image Quality The primary purpose of a medical imaging system is to create images of the internal structures and function of the body to be used for diagnostic or therapeutic monitoring purposes. The degree to which this is possible depends strongly on the quality of the images •Contrast •Resolution •Noise •Artifacts •Distortion •Accuracy—quantitative and/or diagnostic
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Summary of Previous Lecture We defined contrast and introduced the concept of modulation, C=m f =(f max -f min )/(f max +f min ) Local or targeted: C=(f t -f b )/f b Distinguished display contrast adjustment (window, level) from fundamental digital values contrast Using the transfer function for harmonic input, we introduced the modulation transfer function: Discussed how detection depends on contrast-to-noise ratio (CNR) and how “clutter” can also obscure targets and act like structured noise As an introduction to resolution, illustrated what “resolved” means in terms of the FWHM of PSF’s—just resolved when separation=FWHM Discussed how the “cut-off” of the MTF acts as another resolution specification in terms of “line-pairs” (light-dark or sine cycles) per length (mm or cm) Illustrated for LSI systems that can be described as a cascade of subsystems that the overall PSF is the convolution of the individual PSFs, resulting in the overall FWHM being dominated by the widest PSF Stated that the MTF of such a system is the product of the subsystem MTFs 0 ≤ MTF(u) ≤ MTF(0)=1
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Note: Sometimes the PDF is also called the Cumulative Distribution Function
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SNR tells us about overall image quality CNR tells us about detectability of a target
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3.4 “Noise” (also, Expectation or Expected value) 1 ) ( d p N normalized p N (η)d η = probability that η is between η and η+d η
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image quality 2 prelim - 3.0 Basic Imaging PrinciplesImage...

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